1. The Field of the Invention
The present invention relates to an output control apparatus and method designed to output a commanded mechanical and/or electrical output of a field winging type dynamo-electric machine or an induction motor by controlling an exciting current thereof, in particular to a control apparatus and method for supplying an appropriate exciting current is supplied to the field winging type dynamo-electric machine or the induction motor so as to obtain the demanded mechanical and/or electrical output. For example, the above mentioned mechanical and/or electrical outputs of the field winging type dynamo-electric machine or an induction motor are a generation torque and an generation electrical current. Furthermore, the present invention relates to an output control apparatus and method designed to output a commanded mechanical and/or electrical output by controlling an exciting current of a field winging type dynamo-electric machine or an induction motor for use in a motor vehicle.
2. Description of the Prior Art
Automotive vehicles have been equipped with electric generators which are rotated and driven by internal combustion engine. Such an electric generator is mounted on a motor vehicle for the purposes of charging the battery, igniting the engine, lighting up the headlights or winkers, and supplying electrical power to other electrical units that consume electrical power (hereinafter referred to as “electric load”). Also, hybrid vehicles have been familiarized lately. In a hybrid vehicle, activation of the motor vehicle is carried out by an electric motor and the internal combustion engine is driven for the purpose of supplying electrical power to the electric motor.
AC generators have widely been known as such generators to be installed in motor vehicles. Alternatively, introduction of field winding type dynamo-electric generators or motors is now underway taking into account the manageability of output control.
An electric generator generates three-phase alternate current in a stator coil provided to a stator upon rotation of a rotor having a field coil. The three-phase alternate current is rectified by a three-phase bridge rectifier formed of six diodes and outputted as direct current.
The generated voltage of the electric generator is in proportion to the rotation speed of the rotor and the magnitude of exciting current that flows through the field coil. The voltage used for charging the battery or supplying electrical power to various electric loads in the motor vehicle is required to be kept at a given level. The electric generators of conventional art have been provided with output control means for controlling the generation voltage by adjusting the exciting current with the aid of a regulator even when the generation voltage is fluctuated by the fluctuation of the rotation speed of the rotor.
The output control means controls the output of the electric generator by effecting the duty ratio of the exciting current under the pulse width modulation control, that is, to adjust the field current to be supplied to the field winding. Specifically, a target value of the generator output is determined according to a value of electrical power demanded by the electric loads and the battery, and then a target value of the field current is also determined according to the target value of the electric generator output, which is followed by the determination on a duty ratio of the exciting current based on the target value of the field current. Then, on-off control of the switching elements is performed so as to realize the duty ratio of the exciting current. More specifically, the deviation between a detected value and the target value of the battery voltage is typically used to effect feedback control for increasing/decreasing the exciting current.
A method and an apparatus for controlling exciting current based on generation torque control have come to be known recently. In this method, exciting current is controlled according to a value of the exciting current that has been calculated based on a demanded generation torque.
Japanese Patent Laid-Open Nos. 2003-074388 and 2003-284257, and U.S. Pat. No. 6,900,618 each discloses a method for controlling exciting current under generation torque control, in which generation torque is calculated by substituting a detected value of the exciting current and a detection value of the rotation speed of the rotor into a map indicating the relation between at least exciting current, the rotation speed of the rotor and generation torque. In this method, the calculated generation torque of the electric generator is transmitted to an ECU (electronic control unit) of the motor vehicle so as to be used for internal combustion engine control, or a generation electric current calculated in the same manner is used for battery control.
An apparatus for controlling exciting current used for a field winding type dynamo-electric machine for motor vehicle includes: an exciting current detection unit for detecting an exciting current of the field winding type dynamo-electric electric machine to output a detection value of the exciting current; a rotation speed detection unit for detecting the rotation speed of the rotor of the field winding type dynamo-electric electric machine to output a detection value of the rotation speed; a power generation torque calculation unit for estimating the generation torque based on a relation of the detection values of the exciting current and the rotation speed of the rotor and based on the detection value of the exciting current to output the detection value of a generation torque; and an exciting current control unit for supplying an exciting current to the field winding, the exciting current corresponding to an exciting current command value that has been calculated based on the estimation value of the generation torque.
The above apparatus for controlling exciting current used for a field winding type dynamo-electric machine for motor vehicle utilizes the above method for controlling exciting current under generation torque control, in which method, reference is made to a table or a map indicating the relation between exciting current, rotation speed of the rotor and generation torque. This method, however, has suffered a problem of low calculation accuracy in the determined exciting current which is calculated based on a command value of the generation torque. This problem has created another problem that not-a-small error can occur between the demanded generation torque or output electric current and the actually generated generation torque or generation electric current.
Meanwhile, vector control method is widely used as a method for controlling generation torque of an induction motor. In this vector control method, a torque generating mechanism of an induction motor is regarded as being an equivalent to a DC motor. In other words, this method enables instantaneous generation torque control based on the orthogonality between secondary flux linkage and torque component current.
U.S. Pat. No. 5,334,923 (Lorenz et al.) discloses a method and an apparatus for indirectly controlling generation torque of an induction machine based on air-gap flux. Specifically, these method and apparatus carry out control of a space angle made between motor flux, such as rotor flux, and generation torque command current to instantaneously effect generation torque control. More specifically, the method and apparatus of Lorenz et al. control vector quantity which is composed of the amplitude and position components of motor flux, such as rotor flux. Thus, according to the method and apparatus of Lorenz et al., measurement is made of the amplitude and the position of motor flux, such as rotor flux. The rotor flux can be calculated from the air-gap flux. In particular, measurement of third harmonics of the air-gap flux may determine the amplitude and the position of the rotor flux with high accuracy. U.S. Pat. No. 5,272,429 (Lipo et al.) discloses a method for calculating third harmonics of air-gap flux based on stator voltage and current. This method calculates a slip gain error based on the amplitude and the position of rotor flux to correct the exciting current required for compensating the requested generation torque.
However, the methods and apparatuses disclosed in the above patent documents are provided on the assumption that there is a linear relation between the generation torque of an induction machine and the generation torque command current. This raises a problem of insufficiency in the accuracy of the generation torque control in case, for example, where the linearity is broken for some reasons. One of the factors that may cause the non-linearity is magnetic saturation or hysteresis characteristics of a magnetization circuit, or else, the fact that a rotating member which is driven by a motor has inertia weight.